When material to be crushed is introduced in the crushing gap of a gyratory crusher of the type stated by way of introduction, the material causes the inner shell and, thereby, the crushing head to rotate in the direction opposite to the direction of rotation of the eccentric. On the other hand, when no material is supplied the crushing head starts to rotate in the same direction as the eccentric. When the crusher is to be shifted from idle-running to crushing, the rotation of the crushing head must first be decelerated to zero speed and then accelerated for rotation in the opposite direction. This results in considerable wear to the crushing shells. Moreover, the crushing head may reach such a speed, as it co-rotates with the eccentric, that the material to be crushed is thrown out of the crushing gap when new material is being fed to the crusher, which may be hazardous for the operator. To remedy the above problems gyratory crushers are provided with anti-spin assemblies which are adapted to prevent or brake, in different ways, the co-rotation of the crushing head with the eccentric.
Various anti-spin assemblies for gyratory crushers are known in the art.
U.S. Pat. No. 3,887,143 discloses an anti-spin assembly which is arranged at the lower part of the crusher shaft. A hydraulic pump is attached to the anti-spin assembly. A displaceable universal drive shaft extends through the shaft and is connected at its upper portion to a universal joint, which in turn is connected to the crushing head mount. The lower end of the shaft is connected to the internal rotary mechanism of the pump through a coupling. During a no-feed condition when the crushing head starts to rotate with the eccentric in the direction of rotation of the latter, the rotary mechanism of the pump is bypassed to allow only very slow rotation of the shaft and the crushing head. According to that disclosure, the co-rotation of the crushing head with the eccentric is restrained to such an extent by the pump that the shell is not damaged.
U.S. Pat. No. 3,743,193 discloses a hydraulic motor, which is disposed inside the crushing head for rotating the crushing head at the same speed as the eccentric, but in the opposite direction. The result is that the crushing head is essentially stationary at zero load.
WO 01/28689 discloses an anti-rotation and sealing system for a gyratory crusher. A seal is provided between the lower portion of the crushing head and a fixed frame. At its upper end the seal is tightened into the crushing head and rotates with the same. At its lower end the seal is tightened into a clamp element with a plate that is pressed against a surface of the fixed frame by way of a plurality of springs. The purpose of the springs is to provide enough friction between the plate and the surface to prevent the crushing head from rotating when the crushing chamber is empty, while allowing the head to rotate slowly when material is present in the chamber. This is a relatively complex construction, and one that brakes in both directions.